1. Field of the Invention
The present invention generally relates to electric welding and more specifically to methods of electric-arc welding.
2. Description of Related Art
A method of consumable-electrode electric arc welding is in wirespread use nowadays, wherein a consumable electrode is fed into the welding zone, said electrode being in fact a round-section solid wire (of., e.g. `Techniques of electric fusion welding of metals and alloys`, edited by B. Ye. Paton, 1974, (Moscow) pp. 207-211, FIG. 5-50; p. 475, FIG. 9-6, Table 9--9; "Gas-shielded metal-arc welding" by A. G. Potapyevsky, 1974 (Moscow), p. 142, FIG. 55; p. 127, FIG. 49 (in Russian). Used as a shielding medium are a variety of fluxes or gases. Control of the welding current (amperage), size and shape a weld seam, and efficiency of the welding process is effected by varying the rate of feed of a metal-arc electrode into the welding zone, and by changing the welding voltage.
Filling-up of the weld end crater is carried out by appropriately varying the rate of feed of the metal-arc electrode and the value of the welding voltage.
According to the aforementioned electric-arc welding method a preset depth of penetration of the metal being welded is easily attainable due to a broad range of feed rates of a single cross-section metal-arc electrode. However, whenever it becomes necessary to increase the welding current (amperage), efficiency of the welding process and weld seam dimensions (e.g., for welding extra-thick metallic components without bevelled edge in the components being welded together and with a gapless joint therebetween), one must increase the rate of feed of the metal-arc electrode into the welding zone and the welding voltage value. This in turn involves excessive consumption of the welding materials and electric power, an oversize weld and impaired shape and quality of a welded joint of the components being welded together.
Moreover, necessity for a synchronous control of the welding amperage and welding voltage results sophistication of the welding equipment and affects its operating reliability. Filling-up of an end crater of the weld seam also involves complicated equipment, since the filling-up procedure is carried out by simultaneous control of the metal-arc electrode feed rate and of the welding voltage, which deteriorates the quality of the weld seam obtained.
Known in the present state of the welding art is a widely used method of electric-arc welding, wherein a metal-arc electrode fed into the welding zone is composed of two or more bare wires arranged parallel to one another and connected to the same source of welding current (cf., e.g., British Pat. No. 1,280,147, Int.Cl. B3R). All the wires that the electrode is made up of are fed into the welding zone at the same time.
Control of the welding amperage and efficiency of the welding process, and of the size and shape of the weld seam is carried out by varying the rate of feed of a metal-arc electrode into the welding zone and by changing the welding voltage.
According to the electric-arc welding method discussed above a preset depth of penetration of the metal being welded is easily attainable, since preset welding amperage and depth of penetration of the metal being welded correspond to each rate of feed of the metal-arc electrode, while the depth of penetration varies, in this particular case, in direct proportion to the welding amperage or current density effective in the metal-arc electrode. The electric-arc welding method under consideration suffers from a serious disadvantage, that is, the melting rate of the metal-arc electrode changes more intensity than the depth of penetration of the metal being welded, which is evident from the following formula: EQU Q=I.sup.2. R.t,
where
Q - amount of heat evolved by the metal-arc electrode extension; PA1 I - welding amperage; PA1 R - resistance of the electrode extension; PA1 t - time of welding current passing through the metal-arc electrode extension.
This results in too high consumption of the welding materials and electric power and makes it impossible to obtain a weld seam featuring satisfactory dimensions and shape of weld beads within a broad range of weld joint thickness of the components being welded, by virtue of electric-arc welding with a composite metal-arc electrode. Thus, for instance, whenever it is necessary to weld heavy metallic components together using electric-arc welding without bevelling the edges being welded, one must increase the welding amperage, the rate of feed of the composite metal-arc electrode, and the welding voltage.
Since the metal-arc electrode melts more intensely than the metal of the components being welded together, the resultant weld seam features oversized weld bead, unsatisfactory cross-sectional shape, and low quality. This disadvantage of the method is counteracted by prebevelling the edges being welded, which adds mush to the labour requirements for production of an article or structure, and affects the efficiency of the welding process. Filling-up of the weld and crater is carried out by stretching the arc followed by its extinction. The present electric-arc welding method makes no provision for welding variable-size joint edges since, e.g., an increased gap in the butt joint being welded involves higher demand for the metal of a metal-arc electrode, which can be met due to an increased rate of feed of the composite metal-arc electrode. This results in high welding amperage and hence in a proportionally increased arc current density, which is fraught with possible burn-through of the components being welded together.
The method suffers from a disadvantage concerned with a necessity for a synchronous control of the welding amperage and welding voltage, which increases the sophistication of much the welding equipment. Besides, filling-up the weld end crater by stretching the arc adversely affects the quality of the weld seam obtained.